Process for forming transparentized paper containing cotton linter fibers and paper thereof



United States hatent C PRGCESS FQR FORMING TRANSPARENTHZED PAPERQONTAINKNG CQTTON ENTER FIBERS AND PAPER THEREUF Edwin 'GardnerGreennran and Paul Thomas Kitze, Nowell, Wis assignors to Kimberly-(HarkCorporation, Neenah, Wis, a corporation of Delaware N Drawing. FiledJuly 15, 1963, Ser. No. 295,233

9 Claims. .(Cl. 162-135) This invention relates to an improvedtransparentized paper and production methods therefor. Moreparticularly, it relates to the production of improved translucenttracing or diazo intermediate papers containing cotton linters as aneconomical replacement for the more expensive all rag fibers employed inconventional rag tracing papers.

Transparentized tracing papers for engineering drafting and diazointermediate use, traditionally have been made from well-beaten allrag'fibers, internally sized with rosin, top sized with glue in aloftirig operation, and subsequently made translucent by impregnationwith an oil or resin in organic solvent, or by treatment with a hot meltresin.

Preparation of conventional all rag fiber base papers fortransparentized paper is inherently difficult. Fiber formation in thesheet must be clear and uniform. Sizing and density must be rigidlycontrolled to permit subsequent solvent impregnation and yet hold outdiazo solution or ink and provide a good erasing surface.

An object ofthe present invention is to provide a lower costtransparentized or translucent sheet containing cotton linters as theprincipal fibers in the furnish.

A further object is to provide a process for transparentizing a cottonlinter base sheet without the need for supplementary internal or surfacesizing.

Another object is to provide a process for transparentizing paper whichutilizes an aqueous emulsion system and a single saturation srep'ro'obtain transparency, hardness, and good sizing properties.

Conventional tracing papers are made from high quality, strong ragfibers normally obtained by pulping high grade cotton rags such as whitetable cuttings from shirt or similar garment factories. The resultingfibers are relatively easy to hydrate and fibrillate and in the processof preparing base sheets are well beaten or highly refined to producewell-formed hard sheets of high strength subsequently treated to obtaintranslucency therein. A high degree of refining is necessary both toobtain good, clear formation and to develop suflicient fiber-to-fiberbonding to provide the necessary high strength. Without initial highstrength the resulting product is unsatisfactory since the solvent-basedresins or oils used in the conventional transparentizing step tend toweaken the sheet to some extent.

Tracing or diazo intermediate papers are designed primarily to serve asmasters in some type of photochemical copying process, such as blueprintor diazo processes, therefore, these papers should desirably have theability to transmit ultra-violet light readily. This is one of the mainreasons for transparentizing the paper. Since extraneous coloring matterin these papers absorbs ultraviolet light strongly, 'it is important toeliminate such materials from the paper if possible. Many of thebleached rag cuttings used for conventional rag fiber 3,235,443 PatentedFee. 15, 1966 "ice pulps now contain fluorescent dyes, so-called opticalbleaches, whose absorption band nearly always coincides with those ofthe sensitizing chemicals used in photochemical reactions. Thus, thepresence of such dyes cuts down detrimentally on the speed of thereproduction process. At the present time, it is becoming increasinglydifficult to obtain rag cuttings free of such dyes. Since the tracingpapers of this invention avoid using these traditional rag fibers in thefurnish, the possibility of having such undesirable dyes present iseliminated.

Because bleached cotton linters are much less expensive than thebleached rag fibers used in conventional tracing papers, attempts havebeen made in the past to substitute these more economical linters forthe traditional more expensive rag fibers. However, such attempts havebeen largely unsuccessful. Linters have difierent characteristics thanregular textile length cotton fibers used in rag papers. Linters do nothydrate easily, and even when they are beaten severely in an attempt toobtain good binding properties and tight formation, a sheet formed fromcotton linters is not of sufficient hardness and strength fortransparentizing by conventional solventbased materials. Because they donot hydrate easily and develop good binding properties, substitution ofcotton linters for rag fibers in conventional tracing papers and thelike has been satisfactory, heretofore, only up to the extent of about10% to 15% of the total fiber content in the furnish.

By the process of this invention it is now possible to use up to 100%linters, or other short, high alphacellulose content fibers, and obtainsatisfactory tracing papers comparable in physical and opticalproperties to the higher priced all rag fiber papers. While considerablesavings are possible in the original cost of the fibers themselves, itwas found that additional savings could be obtained with a cotton lintersheet because the higher freeness of such fibers usually permits betterdrainage, easier handling on the paper machine, and potentially higherpaper machine speeds. The initially short cotton linter fibers alsopermit good formation. The base sheets thus formed do not have highstrength, even when well-beaten, but since the transparentizer employedin this invention acts as a binder for the fibers in the finished sheet,initial high sheet strength is not necessary. A minor amount of longerand stronger fibers may be added to build up other strength properties,such as tear, without departing from the inventive concept taughtherein.

The transparentizers employed in this invention are aqueous emulsions ofclear, film-forming polymers, instead of the conventionaltransparentizers employed for all rag papers, the latter including oil,resins in organic solution, or hot melt resins. It was found that clearfilmforming polymers not only transparentize the cotton linter ba-sepaper, but also act as binders for the fibers and perform the necessarysizing function as well. Conventional rag base papers do not saturatewell with aqueous emulsions because such papers are normally too hardand close in formation and resist penetration by aqueous media.

While it was found that a large number of aqueous emulsions offilm-forming resins, including many wellknown synthetic latices, werecapable of transparentizing the waterleaf cotton linter base paper,those comprising acrylic material as a major ingredient are preferredbecause of their light color and superior heat and light agingproperties. Although waterleaf cotton linter papers treated with aqueousemulsions of many of the acrylate polymers now commercially availablewere transparentized and sized to a satisfactory degree, many of thepapers so treated had a relatively soft hand, which is suitable for someuses but lacked the snap or rattle generally characteristic of, anddesirable in, hard-beaten all rag papers. For example, when aqueousemulsions of soft, thermoplastic acrylate resins are employed as thesaturant, the paper is satisfactorily transparentized but is relativelylimp. Soft thermoplastic resins of this type are wellknown and includealkyl acrylate polymers and copolymers and copolymers of alkyl acrylatesand styrene. While such paper is suitable for use as a reproductionpaper, it is not generally considered satisfactory for tracing paper usebecause of its lack of hardness and stiffness. Aqueous emulsionscontaining harder acrylic resin mix tures and especially resins of thethermosetting type do produce papers which have the desired hardness andstiffness commonly associated with conventional tracing paper.Accordingly, hard acrylic resins of the thermosetting type comprise thepreferred embodiment when tracing papers are desired.

Compositions of this latter type are described in detail in US. Patent3,033,811, which issued May 8, 1962. As described therein, thesecompositions are prepared by mixing (1) an aqueous dispersion comprisinga copolymer of (a) at least one monomer selected from the groupconsisting of styrene, vinyltoluene, acrylonitrile, and acrylic andmethacrylic acid alkyl esters in which the alkyl group contains from 1to 8 carbon atoms and (b) a monomer selected from the group consistingof acrylamide or methacrylamide, and the formaldehyde reaction productsof said amides including methylol and methoxymethyl derivatives, with(2) a water-soluble thermosetting aminoplast, and (3) a volatiletertiary amine. Preferably, but not necessarily, the mixture may alsoinclude (4) an additive which is a dispersant in the form of an amine orammonium salt of a polymeric carboxylic acid.

As noted in the patent, the aqueous dispersion thus prepared ispreferably, but not necessarily, deionized if Watersoluble ionizablecompounds are present.

Suitable water-soluble thermosetting aminoplasts include the methylolderivates of urea, cyclic ethylene urea, cyclic propylene urea,thiourea, cyclic ethylene thiourea, melamine, alkyl melamines, arylmelamines, guanamine, alkyl guanamines, aryl guanamines, and mixturesthereof.

A preferred class of Water-soluble aminoplasts are the condensates offormaldehyde and the reaction products of urea and malamine with a loweralkanol, such as methanol. These condensates are heat-convertible toinsoluble cross-linked polymers. The condensates of methoxymethylureasand formaldehyde are particularly suitable.

Typical volatile tertiary amines are the trialkylamines containing 3 to12 carbon atoms, triethanolamine, and N- methylmorpholine.Triethanolamine and triethylamine are particularly suitable.

For the dispersant, the ammonium and lower amine salts of polyacrylicand polymethacrylic acids and similar salts of the polymeric acidobtained by copolymerizing methyl vinyl ether with maleic anhydride aresuitable. A particularly preferred mixture employs the ammonium halfamide salt or the diammonium salt of a diisobutylene-maleic anhydridecopolymer having a number average molecular weight of from 2000 to about4000.

A coalescent such as isophorone, Z-ethyl-hexanol, or tributyl phosphatemay also be added to aid fusion of the resln.

As noted previously, cotton linters do not hydrate or fibrillate easily,hence even when well-beaten, do not produce the strong paper normallyconsidered necessary for transparentizing. However, paper made fromwell-beaten linters does have a clear uniform formation, which isessential in producing satisfactory transparentized or translucentpaper. Hitherto it had not been possible to obtain a transparentizedsheet with the hardness, water resistance and ink acceptance requiredfor tracing papers from a bibulous Waterleaf base sheet such as papermade primarily from cotton linters provides. It has been foundunexpectedly that when a relatively weak cotton linter base sheet isimpregnated with an aqueous resin emulsion of the type described herein,the resin intrudes between the fibers, filling the voids therebetween toproduce an optically continuous sheet, and additionally formingfiberresin-fiber bonds, which when cured, provide the desired strength.At the same time, the cured resin imparts a sizing effect to thefinished sheet to make it water resistant, resistant to diazo solvents,and acceptable to ink, while providing a hard, dense sheet resistant topencil embossing. Thus, the simplicity of the single saturation with anaqueous emulsion system employed in this invention to obtainsimultaneous sizing, hardness, and transparency, as opposed toconventional multiple-step sizing and oil or solvent impregnation,results in a highly desirable ease and economy of operation.

To provide a clear uniform formation, the cotton linters, before beingformed into a web, should be well beaten to a Canadian standard freenessvalue of from about to 300. The preferred range of freeness is about to250.

A wet strength resin such as melamine or urea formaldehyde may also beadded to give the web additional strength for subsequent saturation withthe aqueous emulsion of the transparentizing resin.

In the saturating step the transparentizing resin should be added in amanner to deposit in the web between 15 and 30 parts of resin solids per100 parts of fiber. Between 20 and 25 parts of resin solids per 100parts of fiber appear to give the best results.

In one example of the process of this invention, bleached cotton linterswere well beaten to a Canadian standard freeness of about 200, thenformed into a waterleaf sheeet having a basis weight of about 12# per 17x 22-500 sheet ream. The furnish contained about 1%, based on dry fiberweight, of a melamine formaldehyde resin to impart a small degree of wetstrength to the sheet. The wet strength was provided to make the sheeteasier. to handle during saturation.

The waterleaf paper was then saturated, by conventional means, with anaqueous emulsion containing about 25% solids, of a thermosetting acrylicresin composition.

In this case the saturant composition comprised about 100 parts of a 48%solids deionized emulsion of a methyl methacrylate-ethylacrylate-methacrylamide copolymer in the ratio of about 52.5:42.5:5.0respectively, mixed with about 15 parts of an 80% solids aqueoussolution of an aminoplast consisting of a methylatedmelamine-formaldehyde resin, and with about 1 part of triethylamine.Five parts of a coalescent, in this case isophorone, were also used. Adispersant, the ammonium salt of a maleic anhydride-diisobutylenecopolymer with a number average molecular weight of 3000, was also addedin the amount of about 5.5 parts of a 22% solids aqueous solution.

The saturant was retained by the base sheet in the amount of about 23parts by weight per hundred parts of the fiber. After saturation, thesheet was dried on rotat-- ing cylinders maintained at about 230 F. Theheat.

below. The conventional tracing paper was purchased,

8,2 from an office supply store and consisted of 100% rag fibersapparently transparentized with a phthalic polyester resin from solventsolution. The tracing paper also contained a rosin and alum internalsizing and had an animal glue top size.

It will be noted that the lower cost cotton linter sheet is theequivalent of, or better than, the more expensive conventional rag paperin almost every respect except machine direction fold. However, in thislatter property it is still within an acceptable range. The cottonlinter sheet shows a marked decrease in fiuoresence, which accounts forits better performance in print speed. It is also noted that the cottonlinter sheet ages better and actually increases in fold properties withage. This is probably attributable to additional curing of the resin.

While only one specific embodiment of the inventive concept has been setforth herein, it is understood that the invention is not to be construedas limited thereby, and that any suitable changes, modifications, andvariations may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

What is claimed is:

1. A transparentized paper comprising a Web of cotton linter fibers,which fibers have been beaten to a Canadian Standard Freeness of about100 to 300, impregnated with a clear polymeric film-forming acrylicresin of the aqueous emulsion type; said resin being present in theamount of 15 to 30 parts resin solids per 100 parts of fiber; said resinbeing selected from the group consisting of soft thermoplastic acrylicresins and hard thermosetting acrylic resins; said soft thermoplasticresins being selected from the group consisting of alkyl acrylatepolymers and copolymers of alkyl acrylates and styrene, and said hardthermosetting acrylic resins comprising a mixture of (1) a copolymer of(a) at least one monomer selected from the group consisting of styrene,vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkylesters in which the alkyl group contains from 1 to 8 carbon atoms and(b) a monomer selected from the group consisting of acrylamide ormethacrylamide, and the formaldehyde reaction products of said amidesincluding methylol and methoxymethyl derivatives, with (2) awater-soluble, thermosetting aminoplast and (3) a volatile tertiaryamine; said resin binding said fiber together in a substantiallyfiberresin-fiber relationship while substantially filling the voidsbetween said fibers to provide an optically continuous sheet.

2. The transparentized paper of claim 1 in which the 5 resin is a softthermosplastic acrylic resin selected from the group consisting of alkylacrylate polymers and copolymers of alkyl acrylates and styrene.

3. The transparentized paper of claim 1 in which the resin is a hardthermosetting acrylic resin comprising a mixture of (1) a copolymer of(a) at least one monomer selected from the group consisting of styrene,vinyltoluene, acrylonitrile, and acrylic and methacrylic acid alkylesters in which the alkyl group contains from 1 to 8 carbon atoms and(b) a monomer selected from the group consisting of acrylamide ormethacrylarnide, and the formaldehyde reaction products of said amidesincluding methylol and methoxymethyl derivatives, with (2) awater-soluble, thermosetting aminoplast and (3) a volatile tertiaryamine.

4. The transparentized paper of claim 2 in which the resin issubstantially cured.

5. The transparentized paper of claim 3 in which the resin issubstantially cured.

6. A process for manufacturing transparentized paper which comprisesbeating an aqueous suspension of cotton linter fibers to a CanadianStandard Freeness of about to 300; forming from said suspension awaterleaf web comprised of said Well-beaten cotton 1inters; drying saidformed Web; saturating said web with an aqueous emulsion of a polymericfilm-forming acrylic resin in an amount of from 15 to 30 parts resin per100 parts fiber; said resin being selected from the group consisting ofsoft thermoplastic acrylic resins and hard thermosetting acrylic resins;said soft thermoplastic resins being selected from the group consistingof alkyl acrylate polymers and copolymers of alkyl acrylates andstyrene, and said hard thermosetting resins comprising a mixture of 1) acopolymer of (a) at least one monomer selected from the group consistingof styrene, vinyltoluene, acrylonitrile, and acrylic and methacrylicacid alkyl esters in which the alkyl group contains from 1 to 8 carbonatoms and (b) a monomer selected from the group consisting of acrylamideor methac-rylamide, and the formaldehyde reaction products of saidamides including methylol and methoxymethyl derivatives, with (2) aWater-soluble, thermosetting aminoplast and (3) a volatile tertiaryamine; and heating said saturated web sufficiently to dry said Web andcure said resin.

7. The process of claim 6 in which the dried and cured Web issubsequently calendered.

8. The process of claim 6 in which the resin-containing aqueous emulsionis deionized.

9. The process of claim 6 in which about one percent of a melamineformaldehyde resin is added to the aqueous suspension of cotton linterfibers before forming the web therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,629,295 2/ 1953Ruchter et a1 9685 2,999,038 9/1961 Drennen et al 162-168 3,033,8115/1962 Brown et al 260-294 3,105,826 10/1963 Iaggard 117155 OTHERREFERENCES Casey, Pulp and Paper, 2nd Edition, Vol. 1, 1960,Interscience Publishers, Inc., N.Y., page 395.

DONALL H. SYLVESTER, Primary Examiner,

MORRIS O. WOLK, Examiner.

1. A TRANSPARENTIZED PAPER COMPRISING A WEB OF COTTON LINTER FIBERS,WHICH FIBERS HAVE BEEN BEATEN TO A CANADIAN STANDARD FREENESS OF ABOUT100 TO 300, IMPREGNATED WITH A CLEAR POLYMERIC FILM-FORMING ACRYLICRESIN OF THE AQUEOUS EMULSION TYPE; SAID RESIN BEING PRESENT IN THEAMOUNT OF 15 TO 30 PARTS RESIN SOLIDS PER 100 PARTS OF FIBER; SAID RESINBEING SELECTED FROM THE GROUP CONSISTING OF SOFT THERMOPLASTIC ACRYLICRESINS AND HARD THERMOSETTING ACRYLIC RESINS; SAID SOFT THERMOPLASTICRESISN BEING SELECTED FROM THE GROUP CONSISTING OF ALKYL ACRYLATEPOLYMERS AND COPOLYMERS OF ALKYL ACRYLATES AND STYRENE, AND SAID HARDTHERMOSETTING ACRYLIC RESINS COMPRISING A MIXTURE OF (1) A COPOLYMER OF(A) AT LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE,VINYLTOLUENE, ACRYLONITRILE, AND ACRYLIC AND METHACRYLIC ACID ALKYLESTERS IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 8 CARBON ATOMS AND(B) A MONOMER SELECTED FROMTHE GROUP CONSISTING OF ACRYLAMIDE ORMETHYACRYLAMIDE, AND THE FORMALDEHYDE REACTION PRODUCTION OF SAID AMIDESINCLUDING METHYLOL AND METHOXYMETHYL DERIVATIVES, WITH (2) AWATER-SOLUBLE, THERMOSETTING AMINOPLAST AND (3) A VOLATILE TERTIARYAMINE; SAID RESIN BINDING SAID FIBER TOGETHER IN A SUBSTANTIALLYFIBERRESIN-FIBER RELATIONSHIP WHILE SUBSTANTIALLY FILLING THE VOIDSBETWEEN SAID FIBERS TO PROVIDE AN OPTICALLY CONTINUOUS SHEET.
 6. APROCESS FOR MANUFACTURING TRANSPARENTIZED PAPER WHICH COMPRISES BEATINGAN AQUEOUS SUSPENSION OF COTTON LINTER FIBERS TO A CANADIAN STANDARDFREENESS OF ABOUT 100 TO 300; FORMING FROM SAID SUSPENSION A WATERLEAFWEB COMPRISED OF SAID WELL-BEATEN COTON LINTERS; DRYING SAID FORMED WEB;SATURATING SAID WEB WITH AN AQUEOUS EMULSION OF A POLYMRIC FILM-FORMINGACRYLIC RESIN IN AN AMOUNT OF FROM 15 TO 30 PARTS RESIN PER 100 PARTSFIBER; SAID RESIN BEING SELECTED FROMTHE GROUP CONSISTING OF SOFTTHERMOPLASTIC ACRYLIC RESINS AND HARD THERMOSETTING ACRYLIC RESINS; SAIDSOFT THERMOPLASTIC RESINS BEING SELECTED FROM THE GROUP CONSISTING OFALKYL ACRYLATE POLYMERS AND COPOLYMERS OF ALKYL ACRYLATES AND STYRENE,AND SAID HARD THERMOSETTING RESINS COMPRISING A MIXTURE OF (1) ACOPOLYMER OF (A) LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OFSTYRENE, VINYLTOLUENE, ACRYLONITRILE, AND ACRYLIC AND METHACRYLIC ACIDALKYL ESTERS IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 8 CARBON ATOMSAND (B) A MONOMER SELECTED FROMTHE GROUP CONSISTING OF ACRYLAMIDE ORMETHACRYLAMIDE, AND THE FORMALDEHYDE REACTION PRODUCTS OF SAID AMIDESINCLUDING METHYLOL AND METHOXYMETHYL DERIVATIVES, WITH (2) AWATER-SOLUBLE, THERMOSETTING AMINOPLAST AND (3) A VOLATILE TERTIARYAMINE; AND HEATING SAID SATURATED WEB SUFFICIENTLY TO DRY SAID WEB ANCCURE SAID RESIN.